1. Field of the Invention
This invention relates to an image processing apparatus having a function for detecting a special image in an image that has been read. The term "special image" refers to an image such as a bank note or negotiable instrument and so on.
2. Related Art
Recent improvements in the picture quality of copying machines which now have a color capability have been accompanied by the fear of counterfeiting of special originals not meant to be copied. Accordingly, techniques have been proposed which make it possible for the image processor incorporated in such copying machines to recognize a bank note or negotiable instrument itself or an original that contains a special image of this kind (such an original shall be referred to as a "mixed original" below). For example, an apparatus has been proposed in which data characterizing the special image is stored internally in advance, the characterizing data is compared with the characteristics of the entered image signal and it is determined, based upon the result of the comparison, whether the special image is present in the original image.
With this approach, a judgment is made with regard to the degree of similarity between the image data of the mixed original and the image data of the special image, and the data constituting the result of the judgment is subjected to integration in one direction using an integrator in order to eliminate noise.
A drawback encountered in this technique is that since the direction of integration is fixed, as mentioned above, the results of judgment differ depending upon the direction in which the mixed original is read or the orientation of the original.